L. Waldron

50–500 MeV observations of LMC supernova 1987A

Abstract Since the discovery of the supernova outburst in the LMC in 1987, we have made two attempts (on day 55 and day 407) to measure the high energy gamma-ray flux in the range 50–500 MeV, by using a balloon borne spark chamber telescope. On day 55, no positive signal was seen from the source. A 3σ upper limit of 2.9 × 10 −5 ph cm −2 s −1 was obtained after the analysis of the spark chamber data. Preliminary analysis of the quick look data obtained in the second flight shows that the gamma-ray flux even on day 407 was less than 9 × 10 −4 ph cm −2 s −1 (3 σ ).

50–500 MeV γ‐ray emission in the early phase of SN1987A

SN1987A was observed on 19th April 1987 with a combined high energy γ‐ray and hard x‐ray payload, flown on a stratospheric balloon from Alice Springs, Australia. The γ‐ray detector, sensitive in the energy range 50–500 MeV, was an optical spark chamber with 400cm2 area, a field of view of 60° FWHM and a time resolution of 10 μs. The counting rate profile at ∼2.2 mb float altitude has lead to a 3σ upper limit to the steady γ‐ray flux of 7×10−4 ph cm−2 s−1 in the 50–500 MeV range. This upper limit is compared to our predictions for the time profile of γ‐ray emission from SN1987A resulting from pulsar acceleration of particles to cosmic ray energies.

The MART-LIME High-Energy Telescope

MART-LIME is a coded mask imaging hard X-Ray telescope to be flown onboard the international SPECTRUM RG observatory in early 1996. This instrument, the heart of which is a high-pressure proportional counter sensitive to the 5—150 keV energy range, will be characterised by a limiting sensitivity of about 1 milliCrab for a 105 s observation period. The imaging capability of MART-LIME is provided by a coded-mask aperture system, used in conjunction with the position sensitive detector. The basic pattern of the square coded aperture is a 71 x 73 URA mask (twin prime). This is surrounded by an outer frame comprising 17 and 16 pixels, respectively, on adjacent sides, giving a mask of 105 x 105 pixels in total. With this configuration, a fully coded field-of-view of 5.2° x 5.2° is obtained, whilst a partially coded field-of-view is achieved up to 6°, the acceptance angle of the ferrite collimator. The basic concept of the MART-LIME telescope is presented.

Imaging with the MART-LIME telescope on board the Spectrum X satellite

Recent results obtained by balloon and satellite borne coded-mask instruments have been used to simulate the imaging performance of MART-LIME, a coded mask telescope to be flown on board the international observatory SPECTRUM-X-GAMMA on 1995. In particular, we discuss a 6x6 square degree field-of-view centered on the hard X-Ray source responsible for the high energy emission from Galactic Center, at energies above 30 keV. The contributions of GX1+4, GRS1758-25, Terzan 2, Tr 1741-322 and GX354-0 to this field-of-view are also considered. Deconvolved images obtained via the cross-correlation technique are presented. From these images, the limiting sensitivity of the telescope in a crowded sky field is correctly determined.

Performance of the MART-LIME high-energy detector

MART-LIME is a coded mask imaging telescope to be flown onboard the international observatory SPECTRUM X-(Gamma) in 1995. This high-energy instrument, the center of which is a high-pressure proportional counter sensitive to the 5 - 150 keV energy range, will be characterized by a limiting sensitivity of about 1 milliCrab for a 105 s observation period. The imaging capability of the instrument is provided by a coded-mask aperture system, used in conjunction with a position sensitive detector. The basic pattern of the coded aperture is a 71 X 73 URA mask (twin prime). With the addition of an outer frame comprising 18 pixels on each side, a fully coded field-of-view of 2.6 degree(s) X 2.6 degree(s) is obtained, while a partially coded field-of-view is achieved up to 6 degree(s). Test procedures used to determine the performance of the MART-LIME detector are discussed. Results showing the spectroscopic capabilities of a Laboratory-Prototype detector are presented.

SN 1987A - The impact of greater than 50 MeV gamma-ray luminosity limits on theories of particle acceleration

Analysis of the data obtained from two flights of a balloonborne gamma-ray detector to observe SN 1987A was completed. The detector, which included a spark chamber to determine the arrival directions of the photons, was sensitive in the energy range 50-500 MeV. The 95 percent confidence upper limit to the flux on day 55 after the explosion has been established to be 1.1 x 10 exp -5 photons/sq cm/s and on day 407 to be 3.4 x 10 exp -5 photons/sq cm/s. These limits are compared with various theoretical predictions.